With Colombia’s government and the country’s biggest rebel movement announcing an agreement on a historic peace deal, and the Colombian president moving quickly to hold a national referendum on it, The Associated Press explains how the conflict began and developed over the decades.

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HOW IT STARTED

The 1948 assassination of populist firebrand Jorge Eliecer Gaitan led to a political bloodletting known as “The Violence.” Tens of thousands died, and peasant groups joined with communists to arm themselves. A 1964 military attack on their main encampment led to the creation of the Revolutionary Armed Forces of Colombia, or FARC.

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WHAT THE REBELS WANTED

Though nominally Marxist, the FARC’s ideology has never been well defined. It has sought to make the conservative oligarchy share power and prioritized land reform in a country where more than 5 million people have been forcibly displaced, mostly by far-right militias in the service of ranchers, businessmen and drug traffickers. The FARC lost popularity as it turned to kidnapping, extortion and taxes on cocaine production and illegal gold mining to fund its insurgency.

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HOW THE US GOT INVOLVED

In 2000, the United States began sending billions of dollars to counter drug-trafficking and the insurgency under Plan Colombia, which helped security forces weaken the FARC and kill several top commanders. The State Department classifies the group as a terrorist organization and its leaders face U.S. indictments for what the George W. Bush administration called the world’s largest drug-trafficking organization.

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THE MASSIVE HUMAN TOLL

More than 220,000 lives have been lost, most of them civilians. In the past two decades, most of the killings were inflicted by the militias, which made peace with the government in 2003. The FARC abducted ranchers, politicians and soldiers and often held them for years in jungle prison camps. Its captives included former presidential candidate Ingrid Betancourt and three U.S. military contractors, all of whom were rescued in 2008.

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AFTER DECADES OF FALSE STARTS, A PLAN FOR PEACE

Mid-1980s peace talks collapsed after death squads killed at least 3,000 allies of the FARC’s political wing. Another effort fell apart in 2002 after the rebels hijacked an airliner to kidnap a senator. The latest talks had gone on since 2012 in Havana and culminated Wednesday evening with a deal after the last issues were resolved. Agreement previously had been reached on land reform, combatting drug trafficking, the guerrillas’ political participation and punishing war crimes on both sides. In late June, negotiators announced a cease-fire agreement and a blueprint for how an estimated 7,000 FARC fighters will demobilize and lay down their weapons once the peace accord is implemented.